There are several processing contaminants to worry about, that is compounds formed during manufacturing or preparation of food by industry or at home. One of them first came to prominence late in the last century. It had probably been around for a long time as a low-level contaminant very difficult to detect. It was now found at much higher levels in some Asian sauces such as Oyster sauce, Hoisin sauce and Soy sauce. This appearance was due to changes to the manufacturing process of the sauces. Traditionally they were made by slow fermentation, but the process can be speeded up by instead using hydrochloric acid to hydrolyse vegetable protein ingredients like soy protein to achieve the same result. A far cheaper method. And, knowing the food industry, of course this was adopted as the preferred method.
Toxic 3-MCPD formed during heating
We are talking about 3-Monochloropropane-1,2-diol or 3-MCPD for short. It is usually formed when fat-containing foods that also contain salt are exposed to high temperatures during production. It is most frequently found at high levels in soy sauces and the savoury food ingredient acid-hydrolysed vegetable protein. It also occurs at low levels in many other foods and food ingredients as a result of processing. Thus, further studies found 3-MCPD in other heated products like bakery products, malt-derived products, cooked/cured fish or meat, being formed during manufacturing or cooking from lipids and sodium chloride naturally present or added to the food.
In animal experiments 3-MCPD has been shown to be toxic to the kidneys. It has also been shown to induce infertility in rats and suppression of the immune function. Evidence of carcinogenic activity has been found in rats and it has thus been classified as a “possible human carcinogen (group 2B)” by the International Agency for Research on Cancer (IARC). Although not among the worst of the worst, since it doesn’t seem to be genotoxic, it is a contaminant that should be avoided. Thus the Scientific Committee for Food (now European Food Safety Authority) set a level of 2 µg/kg bodyweight for the amount of 3-MCPD which can be consumed daily over a lifetime without appreciable harm to health and this was later supported by the 67th meeting of the Joint FAO/WHO Expert Committee on Food Additives (JECFA).
Since 1996, many regulatory bodies, including those in the European Union, Canada, and several Asian countries, have recommended or required that industry take steps to ensure that 3-MCPD in acid-hydrolysed vegetable protein or Asian-style sauces does not exceed levels ranging from 10 μg/kg to 1,000 μg/kg depending on their views of the seriousness of the compound. A European maximum level of 20 μg/kg has been set on a liquid basis for acid-hydrolysed vegetable protein and Asian sauces calculated on a 40 % dry matter (equal to 50 μg/kg in 100 % dry matter). This same level was also adopted by the Food Standards Australia New Zealand. The USA is using the less stringent level of 1,000 μg/kg for both the dry matter of acid-hydrolysed vegetable protein and for the liquid of Asian sauces.
The situation is a bit complicated in that 3-MCPD can bind to fat molecules to form esters. However, the esters will release free 3-MCPD in our digestive system so the toxicity would be the same. The problem is analytical and how to express the results so that they are comparable. This will still need some harmonisation work to improve accuracy.
New testing results for the presence of 3-MCPD in food reported
Nevertheless, the European Food Safety Authority (EFSA) has now published a report with the latest analytical results from testing by European Union Member States. In total, only 1,235 results covering three years of testing were reported to EFSA and accepted, which is a fairly limited number of results. No 3-MCPD was detected in 59 % of the samples tested which is reassuring. Food manufacturers also seemed to have the production of Asian-style sauces under control with around 80 % of products tested without detectable levels of 3-MCPD and a mean for the products of around 5 μg/kg, well below the allowable level of 20 μg/kg.
The situation was very different for walnut oil with almost 90 % of samples showing detectable levels of 3-MCPD and an enormous mean of 4,750 μg/kg. Luckily we don’t normally consume that much walnut oil. Other vegetable fats and oils had 3-MCPD levels of just a tenth of the walnut oil except for margarine at around 1,500 μg/kg. This is of course still very high and could pose a threat depending on how much is consumed. Most other product categories had 3-MCPD levels below 10 μg/kg with the exception of smoked fish and meat products at around 40 μg/kg. Some food categories had so few samples reported that no credence can be attached to the results.
Based on the results reported, EFSA also calculated an expected population exposure to 3-MCPD. According to a complicated formula EFSA estimates exposure assigned to 64 age and survey groupings for reported food consumption information. The mean exposure to 3-MCPD was less than 1 μg/kg bodyweight per day in most population groups with only four groups showing mean exposure of between 1 and 1.5 μg/kg bodyweight per day. Fortunately, when looking at the exposure covering 95 % of the population, most groups were below the recommended daily intake limit of 2 μg/kg bodyweight, but worryingly eight groups reached exposure of between 2 and 3 μg/kg bodyweight per day.
Vegetable fats and oils and margarine in particular contributed the most to exposure. It would also be worth to have a closer look at bakery products as well as smoked meat that also stood out in contributing to 3-MCPD exposure. Maybe it’s time to tighten regulations covering allowable levels of 3-MCPD also in other food categories than Asian-style sauces to see what industry is capable of achieving.
- 3-MCPD recommendations (Food and Drug Administration, USA)
- 3-MCPD in soy sauce and related products (Food Standards Agency, United Kingdom